Sample rate
Signal Processing and Control Theory
In digital signal processing and in control theory, sampling frequency is the rate at which a continuous-time (analog) signal is sampled into a discrete-time (digital) signal consisting of digital samples. Sampling frequency is usually measured in hertz, or samples per second.
The sample time of a discrete signal can refer either to the period of samples taken from that signal or to the time that a particular sample was taken. In the first case, it is the inverse of the sample rate.
When converting from analog to digital, the analog signal must usually be sampled -- that is, measured or read -- at discrete intervals of time. The length of the interval depends on the application, but is limited by the Nyquist-Shannon sampling theorem. The sampling frequency is the inverse of this number: the smaller the interval, the higher the frequency, and, in general, higher frequencies imply higher-quality sampling.
Audio
In digital audio, common sampling rates are:
- 8000 Hz - telephone, adequate for human speech
- 11025 Hz
- 22050 Hz - radio
- 44100 Hz - compact disc
- 48000 Hz - digital sound used for films and professional audio
- 96000 or 192400 Hz - DVD Audio and Super Audio CD (
Video
In digital video, which uses a CCD as the sensor, the sampling rate is defined the frame/field rate, rather than the notional pixel clock. All modern TV cameras use CCDs, and the image sampling frequency is the repetition rate of the CCD integration period.
- 50 Hz - PAL video
- 60 / 1.001 Hz - NTSC video
When analogue video is converted to digital video, a different sampling process occurs, this time at the pixel frequency. Some common pixel sampling rates are:
See Also
